Production of aluminum oxid.



UNITED s'rirrns PATENT ormcn.

GUSTA'VE scnwnnn, or BELLgIVILL'E, ILLINOIS.

rnonucrxon or ALUMINUM oxm.

No Drawing.

To all whom it may concern; I

Beitdmown that I, GUSTAVE ScmvAHN, a. citizenfiof the United States, and a resident of the city of Belleville, in the county of St. Clair and State of Illinois, have invented certain new and useful Improvements in Processes for the Production of Aluminum Oxid, of which the following is a specification. I I

The aluminum industry, as it exists today, is divisible into two parts, the production of alumina, and the electrolytic reduction of alumina to aluminum.

This invention relates to the first mentioned division, the production of alumina suitable for commercial electrolytic reduction to aluminum, and has for its object the total elimination of sodium'and the reduction in quantity of other impurities in such product.

Alumina to' be of-a quality suitable 'for commercial electrolytic reduction to aluminum must be pure and low'in cost. It must be in a finely divided state suitable for solu- I tion in baths of molten aluminum fiuorids used as an electrolyte in the electrolytic reduction of alumina to aluminum.. The process "hereinafter described produces such alumina in the form of impalp'able powder without grinding or mechanical pulveriz ing, the said alumina being a purer and cheaper ore of aluminum than any heretofore produced.

In the aluminum industry alumina is at this ,time being made from bauxite by a process comprising the use of soda, an Ialuminate of soda being made from the bauxite. Alumina has also been made from cryolite, a double fluorid of aluminum and sodium. the product being substantially free from all impurities with the exception of sodium carbonate. All of the said alumina in commercial use to-day comprises some measure of sodium, which is an objectionable "impurity being reduced with the aluminum and having deleterious efi'ects thereon.

Attempts have been made by men con-' nected-with the aluminum industry, to produce alumina by processes other than those involving. sodium with the object in view. of producing purer and cheaper alumina." These attempts were chiefiy of two kinds One kind comprised endeavors to make use o-f-the fact that alumina may be dissolved Application filed anuary 15,

deposits in Missouri.

markablv-pure, large bodies of it comprising -not more than one per cent. or-two per Specification of Letters ratent. Patented Dial. 23, 1915. i

1912. Serial No. 671,295.

This process contemplates the use of sul- I furic ,acid to dissolve out the alumina from earthy materlals, forming aluminum sulfate, and the subsequent reduction of the aluminum sulfate thus produced to alumina, the sulfuric acid being driven off in such- 7 form that it can readily be used over and over.

Aluminum sulfate may be made from a great variety of earthy materials by this process, and a further object of this invention is the production of alumina suitable i for electrolytic reduction to aluminum from ores hitherto unsuited to the purpose. For example, as this process makes the elimination of silica feasible. it makes new ores. of aluminum available, namely, various aluminum silicates, such as kaolinite. pholerite. and the like, which with moreor less sand and other matters make up bodies of .clay. A good ore, for example. is the non- 3 plastic fire clav or flint-clav found in pocket This material is recent. imourities not being unusual. These. 9 clavs cost materially less per unitof weight of alumina contained therein than bauxite. The cost of the extraction of the alumina from the said clays is less by the process herein described than the cost of extraction 9 of alumina from bauxite by anv soda process per unit of weight ofproduct.

Clay or bauxite is crushed and ground, and heated to alow'. color producing tem- I perture, about 650 degrees centigrade. This treatmentbreaks up the material, adds oxygen to ferrous ironpresent. and makes the:

, alumina more soluble and the iron present less soluble in sulfuric acid. 'lVith some clays, such as Truesdale clay it is advisable 1 to quench the heated, clay in Water after heating. .The clay is .then treated with dilute sulfuric acid which dissolves the, alu- I II mina formine. aluminum sulfate, butdoes out-of clay or baux1te with sulfuric acid.

not dissolve silica. Iron in they-ferric form is n .sulfate Al;(SO,) the product must be pure alumina, provided no impurities, such as sodium, are introduced in the process of desulfurization. Upon heating aluminum sulfate in various ways, it readily parts with a large fraction of the sulfur. Aluminum sulfate, however, holds very 'tenaciously to a small fraction of the said sulfur. The desulfuriza'tion of aluminum sulfate under commercial conditions presents no difficulty till after the sulfur has been reduced to perhaps about 7% of the weight of the product,

but a product comprising sulfur in the.

neighborhood of the said amount is worthless for commercial electrolytic reduction to aluminum. In this process the aluminum sulfate to be treated must be low in free acid, or free from uncombined acid, in order that it may be calcined so as to form a porous mass. The calcination, to produce a porous anhydrous alum num sulfate, must be carried out in a thin mass of the material. The material is then heated to an orange red or medium orange color, the conditions of heating being such that the material is substantially uniformly heated. A temperature of about 1100 degrees centigrade is a good temperature. and alumina. is a non-conductor of heat and a poor retainer of heat. Complete desul- ,furiza'tion apparently depends upon the porous character and thin mass of the aluminum sulfate treated, andupon the means used for conducting heat into the said mass and of the time during which the heating takes place. If during the operation conditions arise causing the material to vitrify, which condition may be indicated by grittimess. the said vitrification prevents further desulfurization. A hard alumina may be formed comprising sulfur, alumina. that it would require the high tem erature of the electric arc furnace to melt. It is one of the features of this process that when properly operated, such vitrification is prevented. Water, water vapor or gas containing hydrogen is brought in contact with and is caused to thoroughly penetrate substantially uniformly heated portions of the material. I The said vapors or gases mav be made topass through stationary material, or may be made o pass across a stream of material, or with or against a stream of the material. One of the'dimensions of the stationary mass or The material, both sulfateto aluminum as carried on commercially.

The chemistry of the process of desulfurlzation is similar to the chemistry of the manufacture of sulfuric acid by the chamber process from brimstone.

Dissociation of the sulfur and alumina is not a simple function of temperature; that is, it does not simply take place suddenly at some fixed and definite temperature regardless of other conditions. It is known to sulfuric acid specialists that in the concentration of sulfuric acid, water dissociates in the presence of sulfur gases at temperatures below those corresponding-to the temper colors ofsteel. Nascent hydrogen and nascent oxygen consequently, no doubt, exist during the carrying out of the process under consideration and one or both of the said nascent gases may play an important part with respect to complete 'desulfurization. The gases formed in the reduction of the sulfate to alumina are collected and conducted into sulfuric acid chambers, where they are treated to form sulfuric acid suitable for use in my process of sulfate making.

The acid used in my process for dissolving alumina is dilute sulfuric acid. lit is commercially correct to make such acid by the chamber process and not by the catalytic process. Consequently, in making-sulfuric acid from the sulfur gases given ofi' by the aluminum sulfate to be used in again dissolving alumina, one of the economical features of the process under consideration,

it is commercially correct, from an acid making standpoint, to use the chamber process. It is consequently unimportant whether the sulfur gases produced are SO, or SO or any other compound of sulfur and oxygen, so long as'the desulfuriza'tion of the aluminum sulfate is complete.

Having described the application of my process commercially, what I claim as of my invention in said process is as follows:

1. The process of producing sodium free alumina in the form of an impalpable powder which consists in treating a thin moving mass of uniformly heated aluminum sulfate with water vapor until all the con- .tained sulfuric acid is removed.

2. The process of producing acid free alumina from sulfate of aluminum which consists in rapidly and uniformly heating aluminum sulfate in a mass of little thickness in comparison with its area of heating surface and passing steam through the heated mass.

3. The process of producing acid free aluminum oxid which consists in uniformly heating to incandescence a relatively thin mass of aluminum sulfate having a large area exposed to the heat, and passing steam through said mass.

4. The process of producing acid free alumina which consists in uniformly heating a wide thin mass of porous aluminum su fate to incandescence in the presence of air and then introducing water vapor as long as the sulfur gases continue to be produced.

5. The process of producing alumina substantially free of sulfur which comprises heating a thin mass of aluminum sulfate in the presence of a moving gas mass comprising highly heated water vapor, said heating being to a temperature hgher than the dissociatinv point of sulfur trioxid.

6. 'fhe process of producing alumina substantially free 4 of sulfur which comprises heating a progressively moving thin mass of aluminum sulfate in the presence of atmoving .gas mass comprising highly heated water vapo'r,.sueh heating being to temperatures higher than the dissociation point of sulfur trioxid. v

Signed at St. Louis, Missouri, this 12t day of January, 1912.

Witnesses:-

A. M. HoLcoMBE, M. A, SHELTON.

GUSTAVE SCHWAHN. 

